1. Friction & Air Resistance

2. Friction
Force that opposes the sliding motion of two surfaces that are touching each other
Direct contact force

3. When two surfaces are in contact, welding or sticking occurs where the bumps from each surface touch
Amount of friction depends on:
Kind of surface
Force pressing surfaces together
Greater the force, greater the microwelds

4. Static friction
Frictional force that prevents two surfaces from sliding past each other.
Unless the force acted on the object is great enough to break the microwelds between the surfaces, the object will not move

5. Air resistance
Friction-like force that opposes motion of objects that move through air
Causes objects to fall with different accelerations and speeds

6. Air Resistance Depends on the size, shape and speed of the object
Not its’ mass!!!
If 2 different massed objects were to be dropped at same time without air resistance they would hit ground at same time

7. Practice Question
What letter represents a feather and apple dropped at the same time in real life?
What letter represents a feather and apple in space or a vacuum where there is no air resistance?

8. Terminal velocity
The faster something falls the greater the force of air resistance
Eventually reach terminal velocity (maximum velocity)
two forces (air resistance and gravity) cancel each other out
Net Force = 0 N
Causes the object to fall at a constant speed (acceleration= 0 m/s2)